Non-volatile memory devices have seen explosive growth with the advancement of electronic applications, such as memory cards, portable electronic devices, cell phones, MP3 players, digital still and video cameras, and other consumer electronics. Application requirements for low cost, power consumption, and high performance are driving memory design to different architectures. Floating gate structures continue to dominate non-volatile memory technology. These structures typically use polysilicon floating gates as the storage node and are arranged in various memory arrays to achieve architectures such as NAND flash and NOR flash memory. To program and erase a memory cell, tunneling methods are used to place charge carriers (i.e., electrons or holes) in the floating gate.
Floating gate transistors are commonly incorporated into non-volatile memory devices such as flash, EPROM, and EEPROM memory devices. For example, floating gate MOSFETs are commonly used in non-volatile memories. A floating gate MOSFET is composed of a MOSFET and one or more capacitors used to couple control voltages to the floating gate. A floating gate is a polysilicon gate surrounded by SiO2. The floating gate may store charge because it is completely surrounded by a high-quality insulator. The charge on the floating gate may be modified, for example, by applying voltages to the source, drain, and control gate terminals to effect Fowler-Nordheim tunneling and hot carrier injection. To maximize efficiency for this type of memory storage, it is desirable to have a high coupling ratio for floating gate memory devices.